Prestressed elastic device with cage and use thereof

ABSTRACT

A prestressed resilient device including a spring ( 1 ) and a prestressing cage ( 2 ) having a variable axial length up to a maximum length (LO) and being inserted inside the spring ( 1 ). The cage ( 2 ) includes two U-shaped distance pieces ( 3, 4 ) that are coupled through their bases that keep the ends ( 11, 12 ) of the spring at a maximum distance apart while enabling them to draw nearer to each other.

[0001] This invention relates generally to a mechanical device, capableof exerting a controlled resilient force.

[0002] More particularly, according to a first aspect, the presentinvention deals with a prestressed resilient device, which comprises aprestressed resilient member exhibiting an elongate shape along an axisand forming an axial passage extending between the first and second endsof said resilient member, and a prestressing cage with a variable axiallength up to a maximum length, such cage being inserted in the axialpassage and resting on the first and second ends of the resilient memberso as to keep them at a maximum distance apart, though enabling them todraw nearer to each other.

[0003] Such devices have been known for decades and used in numeroussectors of mechanical engineering.

[0004] In spite of the relatively simple structures of such devices,there are still some difficulties about their manufacturing, moreespecially in the case of a mass production.

[0005] Therefore, it is an object of this invention to provide aprestressed resilient device, the manufacturing or the assembling ofwhich may be optimized thanks to at least a reduction of the cost of thetooling and/or a reduction of the assembly cycle time.

[0006] To this end, the device according to the invention, which isconsistent with the generic definition as per the introductory parthereinabove, is mainly characterised in that the cage comprises a firstand a second distance piece, each of them having two arms withrespective free ends and respective coupled ends through which they arejoined up together into a common base, the free ends of the arms of thefirst and second distance pieces being bent outwards away from the axisso as to constitute first and second respective flanges which retain thefirst and second ends of the prestressed resilient member, respectively,and wherein the distance pieces are coupled through their bases.

[0007] In a preferred manner, the free ends of the arms of each distancepiece are resiliently biased so as to move away from each other, andaway from the axis, and they are applied onto the prestressed resilientmember.

[0008] Thus, the distance pieces may be fitted the one inside the otherand rest the one on the other by their bases.

[0009] Each distance piece is made, for instance, of a spring steel, andthe prestressed resilient member may be a metal spring and/or a helicalspring.

[0010] Besides, such device may comprise means for the adjustment of themaximum length of the cage.

[0011] Said adjusting means may comprise, e.g., a median fold made inthe base of each distance piece between the arms of said distance piece,and protruding in the direction of the free ends of the arms of thisdistance piece.

[0012] According to a variant, such adjusting means may comprise a boss,made in the base of one of the distance pieces, or a shim placed betweenthe bases of the distance pieces.

[0013] In the latter case, the base of each distance piece mayadvantageously be substantially circular so as to keep the shim inposition.

[0014] The device according to this invention is outstandingly suitablefor the return of a piston of a braking master cylinder.

[0015] Other features and advantages of the present invention will beapparent from the following detailed description, by way of example andby no means as a limitation, when taken in conjunction with theaccompanying drawings, in which:

[0016]FIG. 1 is a perspective view of a device according to theinvention;

[0017]FIG. 2 is a perspective view of a resilient member before it isintegrated into the device according to the invention;

[0018]FIG. 3 is a perspective view of two distance pieces, constitutingthe elements of a cage according to a first variant, prior to theintegration of such cage into the device according to the invention;

[0019]FIG. 4 is a perspective view of two distance pieces, constitutingthe elements of a cage according to a second variant, prior to theintegration of such cage into the device according to the invention; and

[0020]FIG. 5 is a longitudinal sectional view, showing a cage accordingto the invention, comprising length-adjusting means according to apreferred embodiment of the invention.

[0021] As set out hereinbefore, the invention relates to a prestressedresilient device of the type comprising primarily a prestressedresilient member 1, e.g. a helical spring made up of steel, and aprestressing cage 2.

[0022] Whatever the particular shape selected for the prestressedresilient member 1 may be, such member exhibits an elongate shape alonga longitudinal axis X, and it forms an axial passage 10 extendingbetween the ends 11 and 12 of said resilient member 1.

[0023] The prestressing cage 2, having a variable axial length up to amaximum length LO, is fitted inside the axial passage 10 and rests onthe ends 11 and 12 of the spring 1 so as to keep them at a maximumdistance from each other, as set by the maximum length LO of the cage,though enabling these ends 11 and 12 to draw nearer to each other.

[0024] In accordance with the invention, the cage 2 comprises twodistance pieces 3 and 4.

[0025] Each distance piece has two arms, such as 31 and 32 for thedistance piece 3, and 41, 42 for the distance piece 4.

[0026] The two arms of each distance piece comprise respective freeends, such as 310, 320 and 410, 420, and respective coupled ends, suchas 311, 321 and 411, 421.

[0027] Each one of the distance pieces 3 and 4 has a base, such as 30and 40, through which the coupled ends, such as 311, 321 and 411, 421,are joined up together.

[0028] On the opposite side, the free ends 310, 320 and 410, 420 of thearms of the distance pieces 3 and 4 are bent outwards away from the axisX so as to constitute respective flanges, namely 331 for the distancepiece 3 and 432 for the distance piece 4.

[0029]FIG. 1 shows that the function of the flanges 331 and 432, definedby the distance pieces 3 and 4, consists in retaining the correspondingends 11 and 12 of the spring 1, the distance pieces 3 and 4 beingotherwise coupled through their respective bases 30 and 40.

[0030] Each distance piece 3, 4 is, e.g., made up of a spring steel andexhibits resilient properties transversely to the axis X, that is in thedirection corresponding to the mutual closing and opening motions of thearms 31, 32 and 41, 42.

[0031] Therefore, the free ends 310, 320 and 410, 420 of the arms ofeach one of the distance pieces 3 and 4 may be resiliently biased so asto move away from each other and from the axis X, and so as to beapplied onto the inner periphery of each one of the corresponding ends11 and 12 of the spring 1.

[0032] As shown in FIG. 1 too, in a preferred manner, the distancepieces 3 and 4 are merely fitted the one inside the other, with theresult that they rest the one on the other by their respective bases 30and 40.

[0033] Should it be necessary to adjust the maximum length LO of thecage 2, a boss, such as 400 (FIG. 3) may be provided in the base 40 ofone of the distance pieces 3 and 4, so as to bring the flanges 331 and432 closer to each other by a distance corresponding to the height ofsuch boss.

[0034] An alternative (FIG. 4), a shim 5 may be put in between the bases30 and 40 of the distance pieces 3 and 4.

[0035] In the latter case, it may prove convenient that the bases 30 and40 of the distance pieces 3 and 4 exhibit a substantially circularshape, in order to provide a large and stable support for the shim 5.

[0036] Nevertheless, the preferred embodiment of an adjustablemaximum-length cage 20 is represented in FIG. 5.

[0037] In such a cage, the base 30, 40 of each distance piece 3, 4comprises a median fold, such as 301, 401, disposed between the arms 31and 32 or 41 and 42 of the distance piece in question, and protruding inthe direction of the free ends of the arms of these arms.

[0038] Thanks to this arrangement, the mutual bearing of the folds 301and 401 the one on the other provides a knuckle-like contact for thedistance pieces 3 and 4, and the maximum length LO of the cage may beincreased owing to a plastic squeezing of the folds 301 and 401.

[0039] Although the device according to the invention may serve quite anumber of purposes, the most preferred implementation concerns the fieldof hydraulic braking master cylinders, in which the device may carry outthe return of a primary piston and/or of the secondary piston, suchapplication corresponding to a mass production requiring a very highreproducibility of the performance.

1. (Cancelled)
 2. (Cancelled)
 3. (Cancelled)
 4. The resilient deviceaccording to claim 3, characterised in that each distance piece (3, 4)is made up of a spring steel.
 5. The resilient device according to claim4, characterised in that the prestressed resilient member (1) is a metalspring.
 6. The resilient device according to claim 5, characterised inthat the prestressed resilient member (1) is a helical spring.
 7. Theresilient device according to claim 6, characterised in that itcomprises means for the adjustment of the maximum length of the cage. 8.The resilient device according to claim 7, characterised in that saidmeans for the adjustment of the maximum length comprise a median fold(301, 401) made in the base (30, 40) of each distance piece (3, 4)between the arms (31, 32; 41, 42) of said distance piece (3, 4), andprotruding in the direction of the free ends (310, 320; 410, 420) of thearms (31, 32; 41, 42) of this distance piece.
 9. The resilient deviceaccording to claim 7, characterised in that said means for theadjustment of the maximum length comprise a boss (400), made in the base(40) of one of the distance pieces (3, 4).
 10. The resilient deviceaccording to claim 7, characterised in that said means for theadjustment of the maximum length comprise a shim (5), placed between thebases (30, 40) of the distance pieces (3, 4).
 11. The resilient deviceaccording to claim 10, characterised in that the base (30, 40) of eachdistance piece (3, 4) is substantially circular.
 12. The resilientdevice according to claim 13 for returning a piston of a braking mastercylinder.
 13. A prestressed resilient device, comprising a prestressedresilient member (1) exhibiting an elongate shape along an axis (X) andforming an axial passage (10) extending between first and second ends(11, 12) of said resilient member (1), and a prestressing cage (2) witha variable axial length up to a maximum length (LO), said cage beinginserted in said axial passage (10) and resting on the first and secondends (11, 12) of said resilient member (1) so as to keep said ends at amaximum distance apart, though enabling said ends to draw nearer to eachother, characterised in that said cage (2) comprises a first and asecond distance piece (3, 4), each distance piece having two arms (31,32; 41, 42) with respective free ends (310, 320; 410, 420) andrespective coupled ends (311, 321; 411, 421) that are joined up togetherinto a common base (30, 40), the free ends (310, 320; 410, 420) of thearms (31, 32; 41, 42) of the first and second distance pieces (3, 4)being bent outwards away from the axis (X) to constitute first andsecond respective flanges (331; 432) that retain said first and secondends (11, 12) of said prestressed resilient member (1) respectively, andwherein said distance pieces (3, 4) are coupled through their bases (30,40) and said free ends (310, 320; 410, 420) of the arms (31, 32; 41, 42)of each distance piece (3, 4) are resiliently biased so as to move awayfrom each other and away from the axis (X), said distance pieces (3, 4)being fitted the one inside the other and rest on each other at thebases (30, 40) when applied onto said prestressed resilient member (1).